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This study uses a hybrid finite element method to predict dynamic behavior of truncated conical shells with ring stiffeners under fluid loading. The proposed approach combines classical shell theory and the finite element method, making use of displacement functions derived from exact solutions of Sanders' shell equilibrium equations for conical shells. The analysis of the shell-fluid interface involves leveraging the velocity potential, Bernoulli's equation, and impermeability conditions to determine an explicit expression for fluid pressure. To the best of our knowledge, this paper is the first to compare the methods applied to ring-stiffened shells against other numerical and experimental findings. Our results on conical shells in various conditions, with and without ring stiffeners, are largely consistent with previous findings. This study also explores the influence of geometric parameters, stiffener quantity, cone angle, and applied boundary conditions on the natural frequency of fluid-loaded ring-stiffened conical shells. The paper concludes with a discussion of several useful implications for further research. • Vibration analysis of fluid-filled ring-stiffened conical shells. • Finite element method for hydroelastic stability of conical shell. • The solid model based on Sanders' shell theory. • Fluid pressure is expressed using velocity potential and Bernoulli's equation. • Natural frequency is determined for different boundary conditions and geometries. [ABSTRACT FROM AUTHOR]

• A piezoelectric combined cantilever-asymmetric-pendulum structure is proposed. • Can efficiently harvest vibratory energy from any arbitrary direction. • Numerical analysis presented as well as simulation conducted to validate theory and proposed model. • The improvement of the voltage amplitude and operational bandwidth are 128.5 % and 229.8 % over variable excitation amplitudes, respectively. This paper introduces a novel approach to address the challenges faced by traditional unidirectional cantilever-based energy harvesters in adapting to multi-directional vibration environments. The proposed solution combines a flexible cantilever with an asymmetric-conical-pendulum structure which consists of two different concentrated end masses and a rigid thin rod By investigation of energy interchange relationship between the kinetic feature of the asymmetric pendulum and beam bending vibration under horizontal and vertical excitations respectively from base movements, utilizing the Lagrange's theorem and multiple-scale method, 1:2 internal resonance can be induced for enabling the delivery of multi-directional motion of pendulums to the unidirectional bending of cantilever. On this basis, the advantages of the proposed system are revealed by comparing with traditional piezoelectric cantilever and piezoelectric cantilever-single-pendulum systems. Furthermore, the performance of the voltage amplitude and operational bandwidth was potentially improved up to 128.5 % and 229.8 % under x -direction. In addition, it is confirmed that its maximum voltage RMS value is 57.9 % and 11.4 % higher than that of the piezoelectric cantilever-single-pendulum in the x - and z -directions, owing to its multi-peak energy harvesting over variable excitation amplitudes. Therefore, the feasibility and superiorities of the proposed configuration are demonstrated theoretically and numerically in this paper. [ABSTRACT FROM AUTHOR]

• Novel bidirectional full-duplex transmitting WDM-PON over single SSMF is proposed. • SRS + FWM impact on the proposed system performance is evaluated. • SXR-input power, SXR-channel spacing, SXR-channel length variations are simulated. • Results show a reliable communication with the system under SRS + FWM impact. • Proposed system and analyses are important for 5G and beyond fronthaul networks. Wavelength division multiplexing (WDM) is an important method in modern optical communication systems for both long-haul and access networks. Particularly, after being standardized by Telecommunication Standardization Sector of International Telecommunication Union (ITU-T), WDM passive optical network (WDM-PON) becomes a considerable choice for fronthaul implementations of 5G networks. Stimulated Raman scattering (SRS) and four-wave mixing (FWM) are crucial nonlinear impacts that significantly limit the performance of WDM-based optical fiber communication systems. In this paper, an ultra-dense/dense WDM-PON (UDWDM/DWDM-PON) architecture has been proposed and combined dual impact of SRS and FWM on performances of upstream channels (USCs) and downstream channels (DSCs) of the proposed UDWDM/DWDM-PON has been numerically analyzed. USCs have been assumed to operate in 1310 nm region while operating wavelength region of DSCs has been taken as 1550 nm. Simulations have been performed on both UDWDM-PON architectures with 3.125 GHz and 6.25 GHz channel spacings and DWDM-PON architectures with channel spacings between 12.5 GHz and 100 GHz. 2x15-channel and 2x63-channel system structures have been considered in simulations. Signal-to-crosstalk ratio (SXR) has been chosen as performance parameter and its variation with channel input powers, channel spacings and channel lengths have been simulated for both USCs and DSCs of 2x15- and 2x63-channel UDWDM/DWDM-PONs. Results show that the proposed UDWDM/DWDM-PONs using single G.652 fiber can exhibit a reliable communication with minimum 23 dB SXR performance under combined dual impact of SRS and FWM unless some highlights about input powers and channel lengths mentioned in the paper are neglected. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simplify and derive the formulae based on TRL theory and computer programs to demonstrate the relation between parameters. • Derived from the relation of ε' and ε'', a criterion is established to decide what parameters have the possibility of absorbing performance. • A new fitting method is utilized to construct the relation between permittivity and content of absorber. Non-magnetic materials show a great potentiality in microwave absorption with the advantages of low-density, wideband, and thin thickness. Even so, it is still difficult to accurately analyze the connection between performance and parameters. To reveal what electromagnetic parameters could lead to excellent absorbing performance, we simplify and derive the formulae based on Transmission-Reflection-Line theory (TRL) and computer programs. Based on the relation of ε' and ε'', a criterion is established to decide what parameters have the possibility of absorbing performance. Using a new fitting method, the relationship between dielectric constant and absorber content is established. Further, an instruction derived from the relation between ε' and p is used to screen thicknesses. The optimum permittivity of ultra-low reflectivity and ultra-wide band is obtained by combining the numerical analysis results. To verify the accuracy and reliability of results and deductions, the permittivity of four prepared materials and fifty published papers are investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • We have developed a novel workflow to clean up the cryo-electron microscopy datasets directly at the 3D level. • We introduce a modular framework that emphasizes various facets of encoder design for the amortized inference of hidden variables in cryo-electron microscopy image processing. • Our introduced uncertainty measure offers a method to quantify the confidence level of our estimations. • Utilizing contrastive learning significantly bolsters the robustness of orientation estimation. • Incorporating preprocessing layers and employing curriculum learning bolster neural network performance in orientation estimation. In single-particle cryo-electron microscopy (cryo-EM), efficient determination of orientation parameters for particle images poses a significant challenge yet is crucial for reconstructing 3D structures. This task is complicated by the high noise levels in the datasets, which often include outliers, necessitating several time-consuming 2D clean-up processes. Recently, solutions based on deep learning have emerged, offering a more streamlined approach to the traditionally laborious task of orientation estimation. These solutions employ amortized inference, eliminating the need to estimate parameters individually for each image. However, these methods frequently overlook the presence of outliers and may not adequately concentrate on the components used within the network. This paper introduces a novel method using a 10-dimensional feature vector for orientation representation, extracting orientations as unit quaternions with an accompanying uncertainty metric. Furthermore, we propose a unique loss function that considers the pairwise distances between orientations, thereby enhancing the accuracy of our method. Finally, we also comprehensively evaluate the design choices in constructing the encoder network, a topic that has not received sufficient attention in the literature. Our numerical analysis demonstrates that our methodology effectively recovers orientations from 2D cryo-EM images in an end-to-end manner. Notably, the inclusion of uncertainty quantification allows for direct clean-up of the dataset at the 3D level. Lastly, we package our proposed methods into a user-friendly software suite named cryo-forum , designed for easy access by developers. [ABSTRACT FROM AUTHOR]

High-fidelity computation of shock-associated noise places stringent requirements on the accuracy, linear and nonlinear spectral properties of shock-capturing scheme. In this paper, a novel weighted nonlinear compact scheme with seventh-order accuracy is developed for the purpose of improving the linear and nonlinear spectral properties of original scheme (Zhang et al., (2008) [1]). The numerical fluxes at cell centers are obtained using upwind-biased weighted nonlinear interpolation based on the new S-type smoothness indicator that be constant for sine and cosine functions (Wu et al., (2020) [2]). Through systematic spectral analysis and numerical experiments, it is demonstrated that the newly proposed scheme has very weak nonlinear effect and reduces the dissipation and dispersion at the medium and high wavenumbers. The resolution for the short waves and the fine-scale structures is improved. It has the potential to become a suitable candidate for the computation of shock-associated noise. • A novel seventh-order weighted compact scheme named WCOM7S is proposed. • WCOM7S reduces the dissipation and dispersion at medium and high wavenumbers. • WCOM7S has good nonlinear spectral properties and weak nonlinear effect. [ABSTRACT FROM AUTHOR]

Periodic structures feature frequency band gaps in which the propagation of certain waves will be attenuated. Therefore, they are widely applied in the vibration control of structures. The premise of this theory is that the structure should be perfectly periodic. However, this must be broken more or less due to inevitable deviations, leading structures to disorder. The vibration reduction performance can be significantly altered by the disorder, as reported by various authors. Moreover, the disorder pattern plays an important role in such a performance change. In this paper, we study the influence of the disorder patterns and explore a general permutation to retune the disordered periodic structures which means to reduce the deviation of the dynamic characteristics between the nominal and disordered structures. This research is conducted through three stages. In the first stage, a diatomic lumped-mass model is used. We study the implication of the disorder and propose a sorting strategy inspired by global sensitivity analysis (GSA). In the second stage, the sorting strategy is corroborated with numerical simulations by a finite element (FE) model of beam. We use the wave finite element method (WFEM) to calculate the band gaps. A thousand samples are generated randomly to test the sorting strategy and the contrarian strategy. In the third stage, the sorting strategy is verified by an experimental structure of beam. We set up an experimental system and scheme to measure and analyze the effects of the strategy for 5 groups of experiments. We show that vibration suppression may deteriorate statistically due to disorder for periodic structures. Specifically, vibration mitigation is most sensitive to the deviation in the first unit cell from the excitation. Inspired by this finding, a retuning strategy is proposed for the first time, i.e. the unit cell with the smallest deviation should be arranged in the position nearest to the excitation. The results in all stages show that the strategy can significantly improve the similarity of the dynamic characteristics between the nominal and disordered structures. [Display omitted] • Vibration suppression may deteriorate statistically due to disorder for periodic structures. • A retuning strategy is proposed for the first time and verified experimentally. • The unit cell with minimum deviation should be arranged near the excitation. • The influence of disorder is reduced by an order of magnitude after retuning. [ABSTRACT FROM AUTHOR]

This paper presents equivalent deflection as a new concept for bridge damage detection. The equivalent deflection is similar to the real deflection and can be inferred from bridge acceleration measurements (accelerometer). While calculating measured acceleration, the method essentially explores the static response of the bridge to load. It is laid on the premise that most of the deflection response is generally static rather than dynamic. By using the equivalent deflection from a group a trains without knowing their bogie weights, the average single bogie equivalent deflection response (ASBED) can be calculated and used as an indicator of structural damage. Initially, the theoretical procedure is described to find the equivalent deflection from an acceleration signal using a moving force identification algorithm. Then, numerical analyses are carried out to validate the algorithm. The results confirm that the equivalent deflection is close to the real deflection and contains only a small dynamic component. Then, a method to find the shape of influence line is developed. Using real acceleration data from a 26.8 m simply supported railway bridge (located over the West Coast Mainline in Staffordshire, UK), the shapes of equivalent influence lines are obtained from different groups of trains with very good repeatability. The ASBED response concept is introduced as the product of the 'inferred bogie weight' and the shape of the influence line. Good repeatability of the ASBED response is obtained from site with variability less than 1.5%. Theoretically, this ASBED response should be able to detect changes in the influence line when the average bogie weight at the site is repeatable. The last section explores the changes in the theoretical influence line due to different bridge damage conditions by using a 2D grillage bridge model. The results show that a 2% overall reduction in material stiffness or 20% local reduction (over 1.5 m) should be detectable using this method. [ABSTRACT FROM AUTHOR]

Measuring the pantograph–catenary interaction force is crucial for homologation and maintenance purposes. However, this is an intricate procedure that requires a specially-instrumented pantograph. As an alternative to the traditional method of measuring the interaction force, we propose in this paper a new procedure to predict the current collection quality (usually quantified by the standard deviation of the interaction force) from the vertical acceleration measurements of the pantograph collector head. The proposed approach consists of properly preprocessing the acceleration signals to train and validate Artificial Neural Networks (ANNs) to predict the standard deviation of the interaction force. First, the proposed method is defined with academic examples in which different ANNs identify dropper defects and severe contact wire wear from numerically generated pantograph accelerations. The normalization of the input data and proper resampling to make samples independent of the train speed are revealed as key aspects in the success of the proposed approach. Also from a numerical point of view, the method is then applied to predict the standard deviation of the contact force. The results obtained show that these predictions have an error of less than a 10%. The analyses of other potential scenarios such as different train operating speed ranges and the use of displacements instead of acceleration as input, show a poor generalization power of the ANNs used. They provide accurate results only when fed with input samples with the same features as those used in the training stage. Finally, the proposed approach is applied to the experimental data obtained from a pantograph lab test bench. In this case, the ANNs are able to predict the current collection quality with less than a 10% error in almost 95% of the cases. This work aimed to be an intermediate step between pure numerical analysis and real data measured on track. [ABSTRACT FROM AUTHOR]

To comply with the legislation and certification procedures that limit railway noise, reliable approaches are required to reduce the noise from trains. However, effective noise control can only be achieved if the dominant sources are identified first. Beamforming is a possible experimental solution to achieving source identification on a moving train. However, application of the conventional delay-and-sum beamforming method to moving sources relies on the interpolation, or de-dopplerisation, of the received signals, and is therefore computationally expensive. Frequency-domain methods also exist which have been developed based upon the linearisation of the moving trajectory of the source. These are faster in processing time but can only provide accurate source identification within the validity of the linear approximation. They are typically applied to slowly varying sources such as aircraft flyovers. A hybrid beamforming method is presented for application to moving sources with a short pass-by window, which is a typical situation in railway pass-by measurements. The hybrid method proposed in this paper is based on a combination of features of time- and frequency-domain methods. Delays are applied to the signals as in the time domain method and beamforming is performed as for the frequency domain method. It can provide beamforming estimates over a sub-grid by performing de-dopplerisation based on a single point. Numerical simulations and a field measurement targeting a train pantograph are used to compare the performance of three beamforming methods. The numerical analysis of the proposed method shows that, compared with the frequency-domain method, the hybrid approach has more relaxed requirements for linearisation, and thus results in a better beamforming performance. With appropriate settings, a substantial computational advantage can be achieved. The results also show that the conventional method and the hybrid method have a similar beamforming performance, whereas the frequency-domain method shows higher sidelobe level, especially at high frequencies. The proposed hybrid method can achieve both good beamforming performance and low computational cost and can be used as a good alternative of the conventional time-domain method for identification of moving sources. [ABSTRACT FROM AUTHOR]

This article proposes an efficient numerical method for solving nonlinear partial differential equations (PDEs) based on sparse Gaussian processes (SGPs). Gaussian processes (GPs) have been extensively studied for solving PDEs by formulating the problem of finding a reproducing kernel Hilbert space (RKHS) to approximate a PDE solution. The approximated solution lies in the span of base functions generated by evaluating derivatives of different orders of kernels at sample points. However, the RKHS specified by GPs can result in an expensive computational burden due to the cubic computation order of the matrix inverse. We conjecture that a solution exists on a "condensed" subspace that can achieve similar approximation performance, and we propose a SGP-based method to reformulate the optimization problem in the "condensed" subspace. This significantly reduces the computation burden while retaining desirable accuracy. The paper rigorously formulates this problem and provides error analysis and numerical experiments to demonstrate the effectiveness of this method. The numerical experiments show that the SGP method uses fewer than half the uniform samples as inducing points and achieves comparable accuracy to the GP method using the same number of uniform samples, resulting in a significant reduction in computational cost. Our contributions include formulating the nonlinear PDE problem as an optimization problem on a "condensed" subspace of RKHS using SGP, as well as providing an existence proof and rigorous error analysis. Furthermore, our method can be viewed as an extension of the GP method to account for general positive semi-definite kernels. • We propose a new algorithm for solving nonlinear partial differential equations based on sparse Gaussian processes. • Our algorithms base on theories of kernel methods and sparse Gaussian processes. • Our algorithm is meshless and flexible to the shape of domains. • The sparse Gaussian process method reduces computational complexity by using low-rank kernels. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of an efficient predictive density estimation for the density q (‖ y − θ ‖ 2) of Y based on X ∼ p (‖ x − θ ‖ 2) for y , x , θ ∈ R d . The chosen criteria are integrated L 1 loss given by L (θ , q ˆ) = ∫ R d | q ˆ (y) − q (‖ y − θ ‖ 2) | d y , and the associated frequentist risk, for θ ∈ Θ. For absolutely continuous and strictly decreasing q , we establish the inevitability of scale expansion improvements q ˆ c (y ; X) = 1 c d q ( ‖ y − X ‖ 2 / c 2 ) over the plug-in density q ˆ 1 , for a subset of values c ∈ (1 , c 0). The finding is universal with respect to p , q , and d ≥ 2 , and extended to loss functions γ (L (θ , q ˆ)) with strictly increasing γ. The finding is also extended to include scale expansion improvements of more general plug-in densities q ( ‖ y − θ ˆ (X) ‖ 2 ) , when the parameter space Θ is a compact subset of R d. Numerical analyses illustrative of the dominance findings are presented and commented upon. As a complement, we demonstrate that the unimodal assumption on q is necessary with a detailed analysis of cases where the distribution of Y | θ is uniformly distributed on a ball centered about θ. In such cases, we provide a univariate (d = 1) example where the best equivariant estimator is a plug-in estimator, and we obtain cases (for d = 1 , 3) where the plug-in density q ˆ 1 is optimal among all q ˆ c. [ABSTRACT FROM AUTHOR]

While deep learning algorithms demonstrate a great potential in scientific computing, its application to multi-scale problems remains to be a big challenge. This is manifested by the "frequency principle" that neural networks tend to learn low frequency components first. Novel architectures such as multi-scale deep neural network (MscaleDNN) were proposed to alleviate this problem to some extent. In this paper, we construct a subspace decomposition based DNN (dubbed SD2NN) architecture for a class of multi-scale problems by combining MscaleDNN algorithms with traditional numerical analysis ideas. The proposed architecture includes one low frequency normal DNN submodule, and one (or a few) high frequency MscaleDNN submodule(s), which are designed to capture the smooth part and the oscillatory part of the multi-scale solutions simultaneously. We demonstrate that the SD2NN outperforms existing models such as MscaleDNN, through several benchmark multi-scale problems in regular or perforated domains. • We propose SD2NN, a new architecture, combining subspace decomposition from numerical analysis and multiscale DNN solvers. • SD2NN has low/high frequency submodules, simultaneously capturing smooth/oscillatory parts of multi-scale solutions. • The new method outperforms state-of-the-art DNN solvers for 1D-3D multiscale PDEs on regular and perforated domains. [ABSTRACT FROM AUTHOR]

As long-span bridges are usually built at exposed locations and high winds can cause disruptions to traffic, relatively tall wind screens are often used to protect vehicles which are prone to suffer from wind induced accidents. This paper presents the results of a series of two-dimensional discrete vortex method simulations of laminar incompressible flow past standard aerofoil mono-boxes and twin-boxes, conducted to investigate the aerodynamic impact of wind screens on bridge decks in relation to steady-state and divergent instability (classical flutter) behaviour. A comparison against the outcome of a series of parametric wind tunnel tests is also presented. The quality of the agreement between the numerical simulations and the observed experimental behaviour is such that designers, under certain conditions, could rely on computational bridge aerodynamics at feasibility or early design stages to identify potential instabilities and introduce mitigation measures aimed at optimizing the aerodynamic performance of the deck. [ABSTRACT FROM AUTHOR]

This paper considers a coupling of slightly compressible Darcy-Brinkman-transport problem in fractured media with higher Reynolds numbers, involving Brinkman flow in the fractures with advection-diffusion transport in the whole considered media. A new two-layer reduced coupled model is introduced by treating the fracture as hyperplane. The finite difference method with second-order backward differentiation formula and modified upwind scheme by using the fewest nodal points is constructed to solve the new reduced coupled model on staggered nonuniform grids. Based on error derivation of the coupling term, the uniqueness and existence of solutions and second-order convergence rate of numerical method are derived in the mixed forms under the mass conservative transmission and Beavers-Joseph-Saffman conditions. Some experiments are provided to testify the accuracy and efficiency of the numerical method. The numerical analysis of new two-layer reduced model is illustrated to show the behavior of fluid flow and solute transport in the media with intersected, embedded and L-shaped fractures. [ABSTRACT FROM AUTHOR]

• We design photonic crystal fiber with elliptical air holes, which has good orbital angular momentum transmission performance. • The influence of elliptic air hole eccentricity on photonic crystal fiber transmission performance is analyzed. • This paper provides some ideas for new photonic crystal fiber design and air hole shape error analysis. In this paper, a new photonic crystal fiber with elliptical air hole (EAH-PCF) is designed, which can support stable transmission of 80 orbital angular momentum (OAM) modes at 1550 nm. The effective refractive index differences between vector modes are all above 0.002. Most of the modes have a confinement loss between 10−10 dB/m and 10−8 dB/m. The effective mode area of the vector modes are all greater than 70 μm2 and the nonlinear coefficients are all less than 1.8 W−1/km. These properties guarantee high quality OAM. Finally, we discuss the effect of EAH's eccentricity on the PCF. Simulations show that increasing the EAH's eccentricity will increase the degree of separation between the vector modes, but causes a slight decrease in the quality of OAM. [ABSTRACT FROM AUTHOR]

With the growing world population and industrial production, the demand for water has been continuously increasing. By 2030, 60.0% of the world population will not have access to freshwater, which is ∼2.50% of the total global water. For this, a total of over 17,000 operational desalination plants have been constructed worldwide. However, the key barrier to desalination expansion is brine production, which is 50.0% higher than the freshwater, generating 5.0–33.0% of total desalination cost. In this paper, a new theoretical approach for brine treatments has been proposed. It consists in combining electrokinetic and electrochemical mechanisms by using an alkaline clay with high buffering power. Advanced numerical model has been carried out to estimate the ions concentrations in the brine-clay-seawater system. Analytical analyses have been also carried out to estimate the global system efficiency. Results show the feasibility of the theoretical system, its size, and usability of the clay. This model not only should clean the brine to produce new treated seawater but also it should recover useful minerals thank to the electrolysis and precipitations effects. • Innovative brine-clay-seawater system for the brine treatment is proposed. • Electrokinetic principles under applied electrical field are used. • Numerical and analytical analyses have been carried out. • Results provide ion concentrations, feasibility of the system, its size, and usability of the clay. • The brine production is 50.0% higher than the obtained freshwater. [ABSTRACT FROM AUTHOR]

In rotating machinery, non-uniform temperature distribution or hot spots on the rotor surface can induce spiral vibrations. In this paper, a novel experimental apparatus is used to analyze the influence of a hot spot on the dynamic behavior of a flexible rotor supported by oil journal bearings. The hot spot is generated using an induction system with controlled amplitude and phase shift with respect to the vibration vector. Hence, it was possible to mimic phenomena like the Morton effect or the Newkirk effect. Different types of spiral vibrations were experimentally reproduced: stable, unstable and limit cycle. In the latter case, the vibration vector describes a closed loop when plotted in a polar plot. Therefore, the present work isolates the phenomenon of spiral vibrations from the complexity of the physics behind the generation of hot spot whether this source is the viscous shearing, rotor rubbing, or eddy current losses in magnetic bearings. Moreover, a theoretical model is derived to gain insight on the mechanisms driving spiral vibrations especially the role that the phase shift between the hot spot and the vibration vector plays in the stability of the system. Theoretical and experimental stability maps obtained for sub-synchronous and super-synchronous angular speeds are in excellent agreement. Additionally, the notion of thermal period, i.e., the period that govern the oscillation of the vibration vector is introduced. A concept never addressed before. It was found that this thermal period depends not only on the thermal inertia of the rotor, but also on the amplitude and phase shift of the hot spot, the distance to the critical speed and the damping ratio. [ABSTRACT FROM AUTHOR]

• This paper discusses the effect of three types of damping (linear viscous damping, linear hysteretic damping, and nonlinear hysteretic damping) on the isolation performance of Quasi-zero-stiffness system in details. • Two hybrid-damping models, V-H-NH and N-NH model, based on the real engineering applications of QZS system are proposed and analyzed. • The effects of two hybrid-damping models on QZS system are respectively verified by experiments with a hydraulic damper and a TPR damper. A quasi-zero-stiffness (QZS) vibration isolation system was designed to attenuate low-frequency and ultra-low-frequency vibrations. Because nonlinearity exists in QZS systems, various nonlinear dynamic behaviours inevitably influence the vibration isolation performance. Thus, damping is the key for suppressing nonlinear effects. The effects of three types of damping, viscous damping, hysteretic damping, and nonlinear hysteretic damping on the QZS vibration isolator are discussed in this paper. The Duffing-Ueda equation was used to describe the dynamic motion of the QZS system, which was solved using the harmonic balance method (HBM). Two hybrid-damping models were then proposed to avoid unbounded nonlinear responses for excessive base excitation. Based on theoretical and numerical analysis, the effect of the two hybrid damping models, the hysteretic-nonlinear hysteretic (H-NH) damping model and viscous-hysteretic-nonlinear hysteretic (V-H-NH) damping model, on the transmissibility is discussed in detail. To verify the theoretical results, QZS isolator prototypes with two types of hybrid damping were designed and manufactured. A hydraulic damper and a thermoplastic rubber (TPR) damper were used respectively in the two models of the experiments. The experimental results reveal that the isolator with hybrid linear and nonlinear damping provides a better isolation effect for both low-and high-frequency vibrations. [ABSTRACT FROM AUTHOR]

• Extension of the classical Klausmeier model focusing the water flow in flat terrains. • Local dynamics of the diffusive Klausmeier model considering the rainfall rate as a free parameter. • Numerical bifurcation analysis of the diffusive Klausmeier model reveals that the occurrence of spatially inhomogeneous stationary solutions. • Occurrence of vegetation patterns due to the Turing instability as found in field observation. • Minimality of the diffusive Klausmeier model from the viewpoint of a two component reaction-diffusion system. Model-aided understanding of the mechanism of vegetation patterns and desertification is one of the burning issues in the management of sustainable ecosystems. A pioneering model of vegetation patterns was proposed by C. A. Klausmeier in 1999 (Klausmeier, 1999) that involves a downhill flow of water. In this paper, we study the diffusive Klausmeier model that can describe the flow of water in flat terrain incorporating a diffusive flow of water. It consists of a two-component reaction–diffusion system for water and plant biomass. The paper presents a numerical bifurcation analysis of stationary solutions of the diffusive Klausmeier model extensively. We numerically investigate the occurrence of diffusion-driven instability and how this depends on the parameters of the model. Finally, the model predicts some field observed vegetation patterns in a semiarid environment, e.g. spot, stripe (labyrinth), and gap patterns in the transitions from bare soil at low precipitation to homogeneous vegetation at high precipitation. Furthermore, we introduce a two-component reaction–diffusion model considering a bilinear interaction of plant and water instead of their cubic interaction. It is inspected that no diffusion-driven instability occurs as if vegetation patterns can be generated. This confirms that the diffusive Klausmeier model is the minimal reaction–diffusion model for the occurrence of vegetation patterns from the viewpoint of a two-component reaction–diffusion system. [ABSTRACT FROM AUTHOR]

• The measurement data is used to validate the pantograph-catenary model in overlap sections. • Strong dependence on interaction performance of the speed with crossing point height is observed. • Steady arm damper improves the trailing pantograph's performance but sacrifice the leading one's. The overlap section is a railway catenary arrangement where the pantograph transfers from one section to another. In the overlap section, the unsynchronised vibration of two contact wires, contact wire height variation, and elasticity unevenness destabilise the pantograph-interaction performance. This paper presents a systematic investigation of the dynamic behaviours of the pantograph-catenary in an overlap section, including the mathematical modeling, model validation and numerical analysis. In combination with the traditional shape-finding method, an initialization procedure is proposed to accurately describe the crossing point height in an overlap section of a catenary. The measurement data of the maximum uplift of the crossing point collected from the field test in the Gardemobanen line is utilised to validate the pantograph-catenary model in the overlap section. The numerical analysis mainly focuses on the effect of the crossing point height and the inclusion of steady arm damping on the interaction performance at different speeds. The results indicate a strong dependence of the dynamic behaviour in an overlap section on the train speed. A good performance can be achieved with a low crossing point when the speed is much lower than the design speed, while a high crossing point can benefit the transition distance and maximum contact force at high speed. The inclusion of a steady arm damper can improve the pantographs' performance at a low speed. However, the effectiveness degrades with the increase of the train speed, especially for the leading pantograph. [ABSTRACT FROM AUTHOR]

This paper describes a floating-frame-of-reference-based (FFRF-based) recursive formulation for flexible bodies. A new definition of the joint coordinate system is introduced that makes it simpler to formulate more concise velocity transformation matrices. A path matrix, which defines the connectivity of the mechanism for the open loop system, simplifies introducing the topology of the rigid and/or flexible spanning tree. The flexible multibody system is often subjected to large reference motion but small deformations. Both Euler–Bernoulli-based beam (EBB) and continuum-mechanics-based beam (CMB) elements are implemented to validate the proposed approach. The reference conditions mentioned here are used to eliminate the rigid body motion from the deformation field, i.e., removal of the coordinate redundancy, in the FFRF. Thus, different reference conditions, such as simply supported, single-cantilever, and double-cantilever are used. Finally, it is demonstrated that the proposed approach is not limited by the choice of reference conditions, which helps the modeler to apply the approach to different multibody applications. In the numerical analysis, the results of the total energy variation and constraint violations of the close loop systems are fulfilled with good accuracy by using both penalty formulation with augmented Lagrangian method and coordinate partitioning approach for constraint stabilization. Furthermore, the proposed semi-recursive method produces dynamic analysis results comparable to the ANCF with better computational efficiency. In the end, compared to fully recursive approach, the proposed semi-recursive approach shows better efficiency and easier implementation. [ABSTRACT FROM AUTHOR]

During metal cutting, chatter is prone to the effects of poor surface quality and tool wear. Therefore, chatter detection is becoming more and more important. The current hot methods are effective, but they also have limitations, such as the interference of human experience on the results, the need to label the data, and it takes a long time. This paper proposes an unsupervised milling chatter detection method based on a large number of unlabeled dynamic signals. The method does not depend on processing parameters and environment, does not require labels, and has strong stability. Based on auto-encode, each segment of the signal is compressed into two dimensions, and the feasibility of the reconstruction scheme is verified by numerical analysis. In the normalization algorithm, the similarity between the raw signal and the reconstructed signal is the highest, and the reconstruction effect is the best. Then, the compressed signals are clustered based on a hybrid clustering method combining GMM and K-means. Under the six evaluation indicators, compared with GMM, the clustering results of this scheme have been significantly improved. The evaluation metrics show that GMM-K-means is not only more stable but also has better result compared to K-means in chatter detection. The results show that the proposed method outperforms GMM and K-means in all six typical unsupervised evaluation metrics, and can detect chatter effectively. [ABSTRACT FROM AUTHOR]

Three asymptotic limits exist for the Euler equations at low Mach number - purely convective, purely acoustic, and mixed convective-acoustic. Standard collocated density-based numerical schemes for compressible flow are known to fail at low Mach number due to the incorrect asymptotic scaling of the artificial diffusion. Previous studies of this class of schemes have shown a variety of behaviours across the different limits and proposed guidelines for the design of low-Mach schemes. However, these studies have primarily focused on specific discretisations and/or only the convective limit. In this paper, we review the low-Mach behaviour using the modified equations - the continuous Euler equations augmented with artificial diffusion terms - which are representative of a wide range of schemes in this class. By considering both convective and acoustic effects, we show that three diffusion scalings naturally arise. Single- and multiple-scale asymptotic analysis of these scalings shows that many of the important low-Mach features of this class of schemes can be reproduced in a straightforward manner in the continuous setting. As an example, we show that many existing low-Mach Roe-type finite-volume schemes match one of these three scalings. Our analysis corroborates previous analysis of these schemes, and we are able to refine previous guidelines on the design of low-Mach schemes by including both convective and acoustic effects. Discrete analysis and numerical examples demonstrate the behaviour of minimal Roe-type schemes with each of the three scalings for convective, acoustic, and mixed flows. • Asymptotic analysis of numerical schemes at low Mach number. • Consider the convective, acoustic, and mixed convective-acoustic low Mach limits. • Derivation of required asymptotic scaling of artificial diffusion at each limit. • Use of modified equations applies to finite-volume or finite-difference schemes. • Application to Roe schemes shows excellent agreement with previous literature. [ABSTRACT FROM AUTHOR]

• A dual-purpose coupled piezoelectric-electromagnetic structure (DCPES) is proposed. • The electromagnetic element mutually complements with piezoelectric elements. • The dynamic model of the DCPES is established and verified by experiments. • The DCPES harvests energy at low frequencies and isolates vibration above 13 Hz. This paper proposes a dual-purpose coupled piezoelectric-electromagnetic structure (DCPES) for wideband vibration isolation and energy harvesting. It includes two piezoelectric elements and one electromagnetic element, which are used to harvest energy from low-level and low-frequency vibrations and isolate some undesired vibrations. These two combinations result in low resonant frequencies and available nonlinearity. The electromagnetic element mutually complements with piezoelectric elements, and has positive stiffness and hard nonlinearity to damp vibrations with an isolated mass platform. The corresponding dynamic model of the DCPES is established, and the response displacement and output voltage are predicted numerically. In addition, the effects of excitation amplitude, the magnetic constant of the magnet, geometric parameters of the piezoelectric beam, and equivalent mass of the mass platform on displacement transmissibility and output response are explored. More importantly, experimental tests are performed to verify the design and numerical analysis. It is found that the DCPES can efficiently convert vibration energy into electrical energy in a wide frequency range of 5–13 Hz, and successfully dampens oscillations in the frequency range above 13 Hz (the displacement transmissibility is less than 1). The peak output power of the electromagnetic element is up to 15.2 mW, and the total peak output power of two piezoelectric elements reaches 4.6 mW under the excitation amplitude of 0.8 g (g = 9.8 m/s2). Case studies of parameters show that simultaneous wider bandwidth, higher output response, and vibration isolation can be achieved by changing the parameters of the DCPES. [ABSTRACT FROM AUTHOR]

• The relationship between the natural frequency of the blade and the mistuning coefficient is studied. • An improved blade natural frequency deviation-based mistuning identification method with the application of the blade tip timing (BTT) technology is proposed. • Based on the three simplifying assumptions of the fundamental mistuning model (FMM) method, the fourth condition was added and defined: The mode strain energy proportions of the blade in the isolated modal family can be believed identical. • An improved BTT technique-based dynamic strain prediction method is proposed. • Compared with other methods, numerical analysis and experimental investigations verify the feasibility and reliability of this study. Blade tip timing (BTT) is the most effective technique for vibration monitoring of rotating blades. The research of dynamic characteristics and forced responses of the blisk is crucial to the matters of blade vibration with far-reaching significance. The general mistuning identification techniques require experimental tests and numerical solutions of the whole bladed disk. Since the feature of the BTT technique can identify the modal properties of blades, this paper proposed a blade natural frequency deviation-based mistuning identification method, which achieves the mistuning quantitative evaluation and the model online update of mistuned blisk. Numerical analysis and experimental investigations prove that the improved mistuning identification method can reach accurate and reasonable results, especially in the mode dominated by blade vibration. Furthermore, based on the three assumptions of the fundamental mistuning model (FMM), an additional condition was defined: The mode strain energy proportions of the blade in the isolated modal family can be believed identical. This study revealed the relationship between blade strain and blade vibration, and an improved dynamic strain prediction method for the implementation of non-contact measurement of blade strain was proposed. The numerical analysis shows the prediction error of dynamic strain is less than 3%. Two experimental tests reported that the prediction results of dynamic strain are consistent with the FMM and BTT-based non-contact dynamic stress measurement (FB-NDSM) method, and the maximum error of prediction results is less than 2% about a FB-NDSM method reference, which is acceptable in practical applications. Improved mistuning identification and dynamic strain prediction method with the application of BTT technology are attractive for the dynamic characteristic study and health management of the bladed disk, which significantly promotes the application of BTT technology in blade vibration monitoring of large-scale rotating machinery. [ABSTRACT FROM AUTHOR]

This paper develops the structure-preserving finite volume weighted essentially non-oscillatory (WENO) hybrid schemes for the shallow water equations under the arbitrary Lagrangian-Eulerian (ALE) framework, dubbed as ALE-WENO schemes. The WENO hybrid reconstruction is adopted on moving meshes, which distinguishes the smooth, non-smooth, and transition stencils by a simple smoothness detector. To maintain the positivity preserving and the well-balanced properties of the ALE-WENO schemes, we adapt the positivity preserving limiter and the well-balanced approaches on static meshes to moving meshes. The rigorous theoretical analysis and numerical examples demonstrate the high order accuracy and positivity-preserving property of the schemes under the ALE framework. For the well-balanced schemes, it is successful in the unique exact equilibrium preservation and capturing small perturbations of the hydrostatic state well without numerical oscillations near the discontinuity. Moreover, our ALE-WENO hybrid schemes have an advantage over the simulations on static meshes due to the higher resolution interface tracking of the fluid motion. [ABSTRACT FROM AUTHOR]

Multivariate piecewise polynomial functions (or splines) on polyhedral complexes have been extensively studied over the past decades and find applications in diverse areas of applied mathematics including numerical analysis, approximation theory, and computer aided geometric design. In this paper we address various challenges arising in the study of splines with enhanced mixed (super-)smoothness conditions at the vertices and across interior faces of the partition. Such supersmoothness can be imposed but can also appear unexpectedly on certain splines depending on the geometry of the underlying polyhedral partition. Using algebraic tools, a generalization of the Billera–Schenck–Stillman complex that includes the effect of additional smoothness constraints leads to a construction which requires the analysis of ideals generated by products of powers of linear forms in several variables. Specializing to the case of planar triangulations, a combinatorial lower bound on the dimension of splines with supersmoothness at the vertices is presented, and we also show that this lower bound gives the exact dimension in high degree. The methods are further illustrated with several examples. [ABSTRACT FROM AUTHOR]

• New method to calculate response acceleration of structures subjected to impacts. • Verification of the method on a low damped structure by tests and simulations. • Use of various techniques of signal processing to determine the experimental data. • Accuracy of the proposed method is demonstrated by comparison with other options. Shocks and impact loads are generated during the operational life of aerospace vehicles and their effects should be considered for the structural design and verification of these systems. Due to the complexity of assessing shock loads numerically, there is a lack of accurate methods to calculate the mechanical response under a shock environment. One of the existing approaches is the Response Spectrum Analysis, which directly estimates the maximum peak values of structural response accelerations generated by shocks, where it is necessary to define the input acceleration as a Shock Response Spectrum. This approach is based on the calculation of the modal contributions to the total maximum response, which can be combined in different ways, leading to a great variety of possible results for the same response. Furthermore, the existing options generally provide inaccurate results. The objective of this paper is the development and verification of a new method for the Response Spectrum Analysis approach to calculate accurately the peak response accelerations of undamped and low damped structures subjected to impulse base excitations characterized by a main pulse. The proposed method is verified in this paper by numerical analyses for a beam structure to demonstrate the improvement in the accuracy of the provided results compared to the existing options. [ABSTRACT FROM AUTHOR]

In this paper the numerical simulations of the flow around an elastically-mounted circular cylinder with one degree of freedom (1-DOF) with small damping parameter and small mass ratio are presented. The simulations are performed for subcritical Reynolds numbers (2. 0 ⋅ 1 0 3 < Re < 1. 3 < 1 0 4 ), using the URANS (Unsteady Reynolds Averaged Navier Stokes) approach in combination with the SST (Shear Stress Transport) turbulence model. The simulations are carried out on 3D as well as 2D meshes. From the overall results it seems that the bi-dimensional approach could be effectively applied in the lower branch, while major discrepancies are present in the upper branch. The detailed analysis of the wake flow characteristics shows that the three dimensionality of the flow is stronger in the transition zones between the different branches. The extensive comparison between the computational simulations and the experimental results presented in this paper could be considered the "start point" in order to select the proper grid model depending on the requested accuracy. [ABSTRACT FROM AUTHOR]

We present a numerical stability analysis of the immersed boundary (IB) method for a special case which is constructed so that Fourier analysis is applicable. We examine the stability of the immersed boundary method with the discrete Fourier transforms defined differently on the fluid grid and the boundary grid. This approach gives accurate theoretical results about the stability boundary since it takes the effects of the spreading kernel of the immersed boundary method on the numerical stability into account. In this paper, the spreading kernel is the standard 4-point IB delta function. A three-dimensional incompressible viscous flow and a no-slip planar boundary are considered. The case of a planar elastic membrane is also analyzed using the same analysis framework and it serves as an example of many possible generalizations of our theory. We present some numerical results and show that the observed stability behaviors are consistent with what are predicted by the theory. • Fourier Analysis of the numerical stability of the immersed boundary method. • Sharp stability criterion derived and verified computationally. • Practicality of target-point method for modeling no-slip boundaries. • Analysis framework to assess stability of different elasticity models for immersed boundaries. • Use of bandlimitedness in the analysis of the immersed boundary method. [ABSTRACT FROM AUTHOR]

This paper focuses on the numerical analysis of the different wave impacts generated in a wet dam break by varying the downstream depth and the position of the obstacle. With this relatively simple set-up, five hundred impacts were simulated, providing a comprehensive dataset covering the four classical impact types : sloshing, flip-through, aerated and broken wave impacts. We determined the dam break parameters for which the flip-trough impacts occur and showed that among all the flip-through impacts, there is one optimum generating a pressure peak larger that the others. Compared to impact pressures recorded or simulated with a dam break flow in most previous studies, the present numerical work reached values one order of magnitude larger. Therefore with a dam break on wet bottom, it seems possible to generate strong wave impacts in a short duration. This has to be verified experimentally specifically focusing on the measurements repeatability due to the obvious effect of the gate dynamics effect on the subsequent flow. When and if confirmed, this simple set-up could be used to validate numerical models without the need of a long propagation stage before impact. • Numerical study of impacts generated in a dam break varying depth and obstacle position. • All types of wave impacts were obtained through this set-up by adjusting the parameters. • Impact pressures one order of magnitude larger than in previous dam break studies. • Wet dam break may be quick and simple way to generate strong wave impacts. [ABSTRACT FROM AUTHOR]

High-speed planing craft, aircraft when ditching into the water, and ground vehicles entering water can experience violent interaction with the water surface that leads to structural failure. The largest loads typically occur over a very short time, but the magnitude of the pressure and force can be extreme and important for design considerations of safe vehicles. In this paper the water entry problem is studied numerically with one-way and two-way-coupled fluid–structure interaction algorithms. One-way simulations assume a rigid structure while solving for the fluid domain solution, whereas the two-way-coupled approach captures the added mass effects by accounting for the plate deformation in the fluid solution. The primary objectives of this study are to present and validate the numerical methodology, and provide insight into the fundamental physical processes that are important for three-dimensional high-speed aircraft ditching and marine-vessel slamming problems. The fluid solution is obtained using the finite-volume discretization of the incompressible Navier–Stokes equations and the volume-of-fluid method to capture the air–water interface. The structural response is obtained using a modal decomposition representation of the dynamic finite-element system. The fluid–structure-interaction framework is validated by comparison with previously published experimental measurements of an aluminum plate that enters the water with a large horizontal-to-vertical velocity ratio. Several test conditions are discussed that ensure that the numerical solver can capture highly localized pressure maxima, the hydrodynamic force, the behavior of the jet-root propagation, and hydroelastic coupling. Simulation results show the capability to accurately capture these complex phenomena which are important to modeling water-entry problems for the design and certification of air-, land-, and water-craft. [ABSTRACT FROM AUTHOR]

In this paper we present an asymptotically compatible meshfree method for solving nonlocal equations with random coefficients, describing diffusion in heterogeneous media. In particular, the random diffusivity coefficient is described by a finite-dimensional random variable or a truncated combination of random variables with the Karhunen-Loève decomposition, then a probabilistic collocation method (PCM) with sparse grids is employed to sample the stochastic process. On each sample, the deterministic nonlocal diffusion problem is discretized with an optimization-based meshfree quadrature rule. In terms of analysis, we first show the analytic regularity of solutions with respect to parameters in the diffusion coefficients and then present the rigorous convergence analysis for the proposed numerical scheme, i.e., the scheme is asymptotic compatible spatially and achieves an algebraic or sub-exponential convergence rate in the random coefficients space as the number of collocation points grows. These results are further confirmed by a number of benchmark problems. Finally, to validate the applicability of this approach we consider a randomly heterogeneous nonlocal problem with a given spatial correlation structure, demonstrating that the proposed PCM approach achieves substantial speed-up compared to conventional Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Finite-grid (aliasing) instabilities are known to place severe limitations on momentum-conserving particle-in-cell (PIC) methods applied to models including charge separation effects by requiring the resolution of the Debye length. Gyrokinetic models, on the other hand, generally enforce quasi-neutrality thereby removing the Debye length analytically. Recent studies with momentum-conserving PIC applied to gyrokinetic models, however, show that a manifestation of this instability exists in certain physical parameter regimes for arbitrary spatial resolution. In this paper, we show that a simple reformulation of the discrete equations, making use of a co-located discretization of the continuity equation, eliminates this instability for all practical purposes. We perform numerical dispersion analyses for both the original and reformulated schemes, including the effects of finite mean parallel velocity and finite β. We demonstrate that the reformulated scheme is numerically stable for stationary plasmas at any spatial resolution and for plasmas in which the electron mean parallel velocity is smaller than the electron thermal velocity (generally ensured by ambipolarity in plasmas of interest). This reformulation may be particularly useful for codes with complicated meshes, where high-order shape functions or energy-conserving schemes are difficult to implement. The analysis presented here may also be useful for explaining the success of previously considered methods to remove particle instabilities, such as the split-weight scheme. • A detailed numerical analysis for finite-grid instabilities in gyrokinetic particle-in-cell simulations is performed. • A reformulation of the discrete equations is proposed, which eliminates finite-grid instabilities for all practical purposes. • The simplicity of the proposed reformulation may be particularly useful when complicated meshes are involved. • The analysis presented may be useful for understanding the success of certain previously proposed schemes. [ABSTRACT FROM AUTHOR]

In this paper, we study the parkinson oscillation mechanism in a computational model by bifurcation analysis and numerical simulation. Oscillatory activities can be induced by abnormal coupling weights and delays. The bidirectional Hopf bifurcation phenomena are found in simulations, which can uniformly explain the oscillation mechanism in this model. The Hopf1 represents the transition between the low firing rate stable state (SS) and oscillation state (OS), the Hopf2 represents the transition between the high firing rate stable state (HSS) and the OS, the mechanisms of them are different. The Hopf1 and Hopf2 bifurcations both show that when the state transfers from the stable region to the oscillation region, oscillatory activities originate from the beta frequency band or the gamma frequency band. We find that the changing trends of the frequency (DF) and oscillation amplitude (OSAM) are contrary in many cases. The effect of the delay in inhibitory pathways is greater than that of in excitatory pathways, and appropriate delays improve the discharge activation level (DAL) of the system. In all, we infer that oscillations can be induced by the follow factors: 1. Improvement of the DAL of the globus pallidus externa (GPe); 2. Reduce the DAL of the GPe from the HSS or the discharge saturation state; 3. The GPe can also resonate with the subthalamic nucleus (STN). [ABSTRACT FROM AUTHOR]

• A unified dynamic model of eccentric curve-face gear system was established. • Dynamic equation was derived through Lagrange bond diagram. • The dynamic response of the system is a highly nonlinear process • The gear eccentricity can modulate both amplitude and frequency. • Frequency components and amplitudes of different tooth profiles were different. This paper establishes a dynamic model and a Lagrange bond diagram model for the eccentric curve-face gear transmission system. The dynamic model includes a gear meshing model, a lumped-parameter supporting model, a drive and a load, etc. Considering the impact of cam effect and inertia force caused by gear eccentricity, the dynamic equations are established based on the Lagrange bond diagram model. Moreover, the parameters of the model are analyzed deeply, the effects of gear eccentricity, helical angle, tooth profile of gear pairs, and input velocity on the vibration response in time and frequency domain are studied. It is found that the dynamic response of the eccentric curve-face gear transmission system is a highly nonlinear process. The gear eccentricity can modulate both amplitude and frequency. Introducing a force-locking spring in the eccentric curve-face gear transmission system with helical-teeth will negatively affect the system, resulting in the increase of vibration amplitude. The time-varying helical angle of the eccentric curve-face gear transmission system with circle-arc teeth will also have a negative effect on the dynamic characteristics and cause more small pulses. The axial dynamic response, bending dynamic response, and torsion dynamic response are more sensitive than the radical dynamic response to the change of helical angle. Finally, the correctness of numerical analysis was verified through experimental studies. [ABSTRACT FROM AUTHOR]

• Time-domain OD representation of the JCAPL model for wave propagation in porous media • Proof of stability for the JCAPL equivalent fluid model • Stable multipole-based approximation of the equivalent fluid model is built • Multipole-based approximation discretized via a 2D Discontinuous Galerkin scheme • Time-domain resolution of the JCAPL-EFM in a 2D numerical impedance tube The equivalent fluid model (EFM) describes the acoustic properties of rigid porous media by defining the intra-pore fluid phase as a fluid with an effective density and an effective compressibility. Their definitions are based on the dynamic tortuosity α and the normalized dynamic compressibility β. These physical quantities are complex-valued functions depending on the frequency, and can be irrational as in the Johnson-Champoux-Allard-Pride-Lafarge (JCAPL) model. Hence, the system of equations derived from the EFM can involve fractional derivatives in the time domain. This paper presents an approach to formulate the EFM equations described by the JCAPL model in the time domain, leading to an augmented system for which a proof of stability is given. From the EFM, a model for numerical simulation is built with α and β approximated using a multipole model. Sufficient stability conditions are then provided for the multipole-based EFM. Lastly, a numerical analysis is carried out in order to illustrate the theoretical results and a simulation of the impedance tube experiment is presented. [ABSTRACT FROM AUTHOR]

• Developing a vibro-acoustic coupling model for analyses of nonlinear acoustic wave behaviors of vibrational objects. • Numerical tests are carried out to confirm the validity of the developed coupling model. • Physical insights into the effects of high-order vibration responses on the nonlinear acoustic wave in the fluid are provided. • Effects of smooth and non-smooth nonlinearities on acoustic responses of vibrational objects are evaluated. This paper is concerned with numerical analyses of radiated sound behaviors of dynamic systems containing nonlinear vibrational objects immersed in a compressible and inviscid fluid of infinite extent. The vibrational solids are modelled by the Lagrangian description of motion, while the fluid surrounding the vibrational objects is formulated by the two-dimensional linearized Euler equations (LEEs). The nonlinear dynamic responses of the vibrational solids are computed by both the harmonic balance method (HBM) and direct time integration method. A fourth-order dispersion-relation-preserving (DRP) scheme is implemented on a fixed Cartesian grid to solve the governing equations of the fluid. A constrained moving least-squares sharp-interface immersed boundary method is adopted to impose the compatibility conditions on the common boundaries of the vibrational objects and the fluid. Selective filters are employed to suppress the spurious short waves appearing in numerical computations. Several numerical tests are carried out to confirm the validity of the developed vibro-acoustic coupling computational model by comparing the present solutions with the exact solutions. Nonlinear acoustic wave responses of vibrational objects with smooth and non-smooth nonlinearities are examined, including rigid cylinder-shaped oscillators resting on nonlinear mounts, ellipse-shaped objects suspended on nonlinear torsional springs, and rigid isolators with frictions and clearances. It is found that for vibrational objects containing nonlinearities, the amplitude-frequency responses of radiated sound pressure exhibit shifting resonance frequencies, secondary resonances and jump phenomenon. The intermittent collisions of the vibrational objects with clearances can result in abrupt fluctuations and distortions of the radiated acoustic waves in fluid. In addition, the radiation efficiency of high-order harmonics of nonlinear acoustic waves induced by stick/slip transitions of friction interfaces can reach to maximum with the friction coefficient. [ABSTRACT FROM AUTHOR]

• A two dimensional (2D) mesoscale homogenization numerical concrete modelling approach with randomly distributed aggregates with different shapes is proposed. • Effect of local mesoscale structure of concrete on stress wave fields is investigated with both mesoscale models and their homogenization models. • The efficiency of the homogenization approach is illustrated. • Mesoscale multi-physics simulation and test results show that the embedded PZT sensor response is dominatly affected by the interface debonding rather than the mesoscale structure of concrere. In this paper, in order to distinguish the influence of both interface debonding defect and the mesoscale structure of concrete core on the stress wave field and the response of an embedded Piezoelectric-lead-zirconate-titanate (PZT) sensor in rectangular concrete filled steel tube (RCFST) members efficiently, a two dimensional (2D) mesoscale numerical concrete homogenization approach for concrete core considering the random distribution of circular, elliptical and irregular polygonal aggregates is proposed firstly. Then, mesoscale simulation on stress wave fields within the cross-section of RCFST members with and without interface debonding defects using both mesoscale models and their homogenization models are carried out, respectively. The effect of both mesoscale structure of concrete core and the interface debonding defects on the stress wave field of each member is discussed and the efficiency of the homogenization approach is illustrated. Therefore, the time-domain response of an PZT sensor embedded in the concrete core of RCFST members coupled with PZT patches under sweep frequency excitation signal is determined with multi-physics field simulation and compared when both mesoscale models and their homogenization models are used. Then, the sensitivity of the wavelet packet energy of the embedded PZT sensor response on the variation of both mesoscale structure of concrete core and the dimension of interface debonding defects is investigated in details. Finally, in order to illustrate the difference in the significance of the effect of interface debonding defect and the mesoscale structure of concrete core on stress wave propagation, comparative test with a set of RCFST members without and with interface debonding defects is carried out. Test results also show that the influence of interface debonding defects on embedded PZT sensor response and the stress wave fields is dominant. The detectability of interface debonding detection approach using stress wave measurement is illustrated efficiently with the proposed equivalent homogenization mesoscale modelling approach even the mesoscale structure of the concrete core is considered. [ABSTRACT FROM AUTHOR]

• A linearly operator splitting algorithm is proposed for the nonlocal VCH equation. • The energy stabilities for both subproblems are proved. • The stability and convergence of the operator splitting algorithm are studied. • A semi-implicit SDC method is further used to improve time accuracy. Recently, the viscous Cahn-Hilliard (VCH) equation has been proposed as a phenomenological continuum model for phase separation in glass and polymer systems where intermolecular friction forces become important. Compared with the classical local VCH model, the nonlocal VCH model equipped with nonlocal diffusion operator can describe more practical phenomena for modeling phase transitions of microstructures in materials. This paper presents a high order fast explicit method based on operator splitting and spectral deferred correction (SDC) for solving the nonlocal VCH equation. We start with a second-order operator splitting spectral scheme, which is based on the Fourier spectral method and the strong stability preserving Runge-Kutta (SSP-RK) method. The scheme takes advantage of applying the fast Fourier transform (FFT) and avoiding nonlinear iteration. The stability and convergence analysis of the obtained numerical scheme are analyzed. To improve the temporal accuracy, the semi-implicit SDC method is then introduced. Various numerical simulations are performed to validate the accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

• Synchronous theory of the proposed system is given. • Relation of structure and synchronization is analyzed by theory and experiment. • Dynamic characteristics of the system are discussed through the simulations. • Experimental prototype is designed to verify the correctness of theory. The present work is a lucubration and verification of the previous research through theory and experiment. Because of the physical model of the published paper is oversimplified, the revised model is proposed in present research. And the small parameter averaging method and Routh-Hurwitz criterion are adopted to investigate the stability criterion and synchronization condition. Numerical analyses are given to discuss the relation between synchronous characteristics and structural parameters of the vibrating system. And then some simulations are given to research the synchronous mechanism of the system. Besides, an experimental platform is set up to test the dynamic characteristics and synchronization, which verifies the correctness of theoretical analysis and numerical simulations. The theory, numerical simulation and experiment demonstrate that the synchronous state of two identical rotors mounted symmetrically is independent on the variation of installation positions of two exciters. Finally, the error of the experiment datum is analyzed. This study will provide theoretical reference for the design of secondary isolation vibration screen. [ABSTRACT FROM AUTHOR]

• SD-ADER is a new arbitrary high-order method for the induction equation. • It can be seen as a high-order extension of the Constrained Transport (CT) method. • In SD-ADER, the B-field is provably divergence-free (both locally and globally). • Numerical results of SD-ADER are similar to the RKDG with divergence cleaning. • SD-ADER does not need additional equations/variables to control the divergence. We study in this paper three variants of the high-order Discontinuous Galerkin (DG) method with Runge-Kutta (RK) time integration for the induction equation, analysing their ability to preserve the divergence-free constraint of the magnetic field. To quantify divergence errors, we use a norm based on both a surface term, measuring global divergence errors, and a volume term, measuring local divergence errors. This leads us to design a new, arbitrary high-order numerical scheme for the induction equation in multiple space dimensions, based on a modification of the Spectral Difference (SD) method [1] with ADER time integration [2]. It appears as a natural extension of the Constrained Transport (CT) method. We show that it preserves ∇ ⋅ B → = 0 exactly by construction, both in a local and a global sense. We compare our new method to the 3 RKDG variants and show that the magnetic energy evolution and the solution maps of our new SD-ADER scheme are qualitatively similar to the RKDG variant with divergence cleaning, but without the need for an additional equation and an extra variable to control the divergence errors. [ABSTRACT FROM AUTHOR]

• The piezo-metastructure is shunted with a one-way electrical transmission line. • Local-resonance bandgaps are maintained in opposite directions. • Nonreciprocal wave attenuation behaviors exist in the bandgap. • The presented nonreciprocal system is linear, adaptive and easily implemented. • Theoretical and experimental results verify nonreciprocity of the system. In contrary to elastic media, it is easy to attain one-way coupling feature among electrical elements, which enables unidirectional transmission of electrical wave. In this paper, we explore and exploit the interaction of a piezoelectric beam with a one-way electrical transmission line to facilitate nonreciprocal transmission of elastic wave in the linear fashion. Theoretical dispersion analysis and numerical simulations are performed to reveal transmission behaviors of elastic wave in the presented piezoelectric metastructure. It is uncovered that, when the one-way electrical coupling feature is introduced, local-resonance bandgaps are maintained in opposite directions of the piezoelectric metastructure. However, the bandgap attenuation capability in one direction is increased compared to conventional local-resonance metastructures, in which no electrical coupling exists between cells, while that in the other direction is decreased. Therefore, nonreciprocal transmission of elastic wave emerges in this system due to the distinct bandgap attenuation capability in opposite directions. It is also revealed that this sort of nonreciprocal wave attenuation capability is adaptive with the one-way electrical coupling coefficient and the resistance of electrical cells. An experimental set-up of the piezoelectric metastructure is built and experimental results verify the nonreciprocity property and its adaptiveness. Overall, the presented piezoelectric metastructure provides a linear and concise approach to realize adaptive nonreciprocal transmission of elastic wave. [ABSTRACT FROM AUTHOR]